protein trafficking and localization proteins synthesized in cytoplasm, but become localized in...
TRANSCRIPT
PROTEIN TRAFFICKING AND LOCALIZATION
l PROTEINS SYNTHESIZED IN CYTOPLASM, BUTl BECOME LOCALIZED IN l CYTOPLASMl CYTOPLASMIC MEMBRANEl PERIPLASMl OUTER MEMBRANEl RELEASED IN ENVIRONMENT
l HOW? WHAT IS MECHANISM(S) OF LOCALIZATION?
INSERTION OF INTEGRAL CYTOPLASMIC MEMBRANE PROTEINS – AN EXAMPLE
l CYTOPLASMIC MEMBRANE PROTEINS CONTAIN “SIGNAL SEQUENCE” -15 - 30 HYDROPHOBIC AMINO ACID RESIDUES NEAR THE N-TERMINUS
[e.g., GLYCINE, ALANINE, VALINE, LEUCINE, PHENYLALANINE]SIGNAL SEQUENCE ALLOWS PROTEIN TO BIND MEMBRANE AND BE SOLUBLE IN THE PHOSPHOLIPID MATRIX.
l AND TRANS-MEMBRANE-SPANNING SEQUENCES - HYDROPHOBIC
l SIGNAL RECOGNITION PARTICLE SRP BINDS NASCENT PROTEIN (BEING TRANSLATED) AND DELIVERS TO MEMBRANE BOUND RECEPTOR
l RECEPTOR PROTEIN DELIVERS NASCENT MEMBRANE PROTEIN TO TRANSLOCON
l TRANSLOCON INSERTS NASCENT MEMBRANE PROTEIN INTO CYTOPLASMIC MEMBRANE WITH MEMBRANE-SPANNING REGIONS
TRAVERSING MEMBRANE
NASCENT INTEGRALMEMBRANE PROTEIN
RIBOSOMEmRNA
CYTOPLASMICMEMBRANE
RECEPTOR
1 PROTEIN SYNTHESIS STARTS ON RIBOSOME [N-TERMINUS SYNTHESIZED
FIRST]
2 SRP BINDS SIGNAL AND
TRANSPORTS TO RECEPTOR
3 RECEPTOR FACILITATES NASCENT PROTEIN BINDING TO
TRANSLOCON4 TRANSLOCON FACILITATES
INSERTION INTO CYTOPLASMIC MEMBRANE (SIGNAL &
MEMBRANE-SPANNING)
PERIPLASM
SRP
TRANSLOCON
MEMBRANESPANNING
SIGNALSEQUENCE
NADH DEHYDROGENASE
CYTOPLASM
CM
MEMBRANE SPANNINGSEQUENCES APPRECIATE!!
PROTEIN EXPORT INTO PERIPLASMIC SPACE FOUR NECESSARY COMPONENTS IN MECHANISM
l SIGNAL SEQUENCE WHICH IS CLEAVED - [NEAR N-TERMINAL]:
l SOME HYDROPHILIC AMINO ACIDS [e.g., ARGININE, GLUTAMATE]
l FOLLOWED BY HYDROPHOBIC AMINO ACIDS
l FOLLOWED BY ALANINE/X/ALANINE
l CYTOPLASMIC CHAPERONE TO PRESENT UN-FOLDED PROTEIN TO TRANSLOCON
l TRANSLOCON IN CYTOPLASMIC MEMBRANE TO TRANSLOCATE PROTEIN ACROSS CYTOPLASMIC MEMBRANE [N-TERMINUS FIRST]
l SIGNAL PEPTIDASE - ENZYME WHICH CLEAVES OFF THE SIGNAL AFTER ALANINE/X/ALANINE
12
3
4 5
RIBOSOME
mRNA
CHAPERONE DELIVERS UNFOLDED PROTEIN TO TRANSLOCON
SIGNAL PROTEIN DESTINED FOR PERIPLASM
TRANSLOCON - PUMPS PROTEIN THROUGH CELL MEMBRANE. N-TERMINUS EMBEDDED IN CELL MEMBRANE.
SIGNAL PEPTIDASE
CYTOPLASM
PERIPLASM
CYTOPLASMICMEMBRANE
SIGNAL SEQUENCE CLEAVED ANDPROTEIN FOLDS IN PERIPLASM
SIGNAL SEQUENCE COMPLETELY DEGRADED
N
TRANSLOCON
PILUS ASSEMBLY:CHAPERONE - USHER PATHWAY
l P PILI - COMPOSED OF SIX STRUCTUAL PROTEINS
l ALL SIX TRANSPORTED ACROSS CYTOPLASMIC
MEMBRANE
l CHAPERONE CATALYZES PROPER FOLDING IN PERIPLALSM
AND DELIVERS SUBUNITS TO USHER IN OUTER MEMBRANE
PERIPLASMIC CHAPERONE CONDUCTS TO USHER
EXPORT ACROSS CYTOPLASMIC MEMBRANE
OUTER MEMBRANE
PILUS
USHER (PORE)
PILINMOLECULES
LINKERS
ADHESIN
CYTOPLASM
CHANNEL
TAKE AWAY:UNDERSTAND – PROTEINS MUST BE LOCALIZED TO
PERFORM THEIR FUNCTION.
CYTOPLASMIC MEMBRANE LOCALIZATION – STEPS & FACTORS INVOLVED
PERIPLASMIC SPACE LOCALIZATION – STEPS & FACTORS INVOLVED
PILUS ASSEMBLY
HOW ARE THOSE PROTEINS RECOGNIZED/MARKED FOR THOSE DESTINATIONS? WHAT ARE THE SIGNALS? WHAT FACTORS RECOGNIZE & ACT ON THE SIGNALS?